The present invention relates to fuel tank filters, and more particularly to filters for use in a fuel tank where the fuel pump is housed inside the fuel tank and the fuel level sometimes falls below the bottom of the fuel pump.
Since the advent of fuel injected automobile engines, fuel pumps have been located inside of the automobile's fuel tank. Typically, the fuel pump is connected to a bracket on the top of the tank. Fuel lines, wires and other connectors may then be made to the pump through the top of the fuel tank. Generally, the fuel system is a closed system. Therefore, the fuel pump is rigidly fixed to the top of the tank to simplify sealing holes in the top of the tank through which the connections are made.
At present, with metal fuel tanks, the fuel pump inlet and a filter on that inlet remain submerged at the bottom of the fuel tank. The pump is typically designed to have its bottom inlet about one-half inch above the bottom of the tank. The rigidity of the metal tank assures that the distance between the top and bottom of the tank, and thus the one-half inch spacing, changes very little. The filters are designed to provide a "wicking" action so that even if the fuel level drops below the bottom of the pump inlet, such as during turning, stopping or hill climbing maneuvers, vapor will not enter the fuel pump inlet.
There is a current desire to change to plastic fuel tanks. These tanks are less rigid, and with thermal contraction and expansion, the distance between the top and bottom of the tanks has known to vary by as much as an inch. Since the pump is fixed to the top of the tank, an increase of an inch in the distance between the top and bottom of the tank results in the bottom of the fuel pump sometimes being more than one inch off the bottom of the tank. If the fuel depth in the tank is low at the same time the tank has expanded, the bottom of the fuel pump may be too far above the fuel for even the wicking action to provide fuel to the pump inlet. The fact that the bottom of the tank moves up and down, coupled with a requirement that fuel always be available at the pump inlet, presents a problem.
One attempted solution to this problem has been to use a fuel tank filter made out of an envelope of filtration material with an internal plastic separator. The separator is flexible, and biased so that it holds the filter envelope on the bottom of the tank. While this concept appears sound, the filters manufactured according to this design have not solved the problem. Tests conducted in developing the present invention show that the plastic used to construct the separator loses its flexibility after exposure to gasoline containing alcohol.